Two air force generals have been authorised to shoot down commercial airliners that appear to be threatening any city in the United States, Pentagon officials said yesterday.

The powers to take out possible hijacked planes were part of a big crackdown on airline security revealed by President George Bush in Chicago yesterday.

It also includes a dramatic increase in the number of armed US marshals travelling undercover on commercial flights to protect against terrorism and boost the nation's confidence in flying.

Other proposals to emerge from the wake of the attacks on the World Trade Centre and the Pentagon include technology that will allow air traffic controllers to take over and land "distressed aircraft" by remote control.

At a conference for airline industry workers at O'Hare airport that became more like a political rally, Mr Bush said his administration wanted "to make sure that anybody who wants to harm America will have a hard time doing so".

He announced that security at US airports would be taken out of the hands of private security companies and placed with the federal government, and members of the national guard would be called up to provide extra airport security.

"Enhanced cockpit protection" will mean that video cameras will be installed in every plane cockpit so that pilots can see what is going on in the cabin. Doors to the cockpit will be fortified and provided with stronger locks.

It will also be ensured that transponders, which signal the plane's whereabouts, cannot be turned off as they were in the planes that were hijacked. About $500m will be spent on modifications to planes. General airline security will be given $3bn in funding.

Mr Bush's measures, which will be introduced as soon as possible, were aimed at restoring confidence. Yesterday, he asked the American public to get back on the planes and travel: "Get down to Disney World in Florida, take your families and enjoy life the way we want it to be enjoyed. We will put the federal government in charge of passenger and bag screening and all safety inspections," he added. "[We will introduce] visible security measures so the travelling public will know that we are serious about airline safety in America."

He said: "We are making a strong statement, that together the government and private sector will make flying a way of life again in America."

Earlier, the Pentagon confirmed that two air force generals had been authorised to order the military to shoot down any civilian plane that appears to be threatening US cities. The defence secretary, Donald Rumsfeld, said he had crafted the new rules of engagement with General Henry Shelton, chairman of the joint chiefs of staff.

Asked what assurance passengers would have against mistakes, he stressed that the generals would only act without executive authorisation in the most extraordinary circumstances and only if there was not enough time to consult.